1. Field of the Invention
This invention relates to a construction cost estimation process, and more particularly to a construction cost estimation process for residential construction.
2. Description of the Related Art
Cost estimation of construction projects for both residential and commercial construction is a necessary step in budgeting for, and constructing, a residential or commercial building. Current early stage cost estimation is at best an inexact science, providing a “ball-park” figure that often leads to erroneous assumptions and cost overruns on any given project.
In the commercial construction industry, efforts have been made to develop a uniform standard classification for various building elements known as UNIFORMAT originally developed by the American Institute of Architects and General Services Administration in 1972 for estimating and design cost analysis for commercial buildings. A second generation of the UNIFORMAT system known as UNIFORMAT II defines a standard classification for building elements and related site work and was released in 1993 by the American Society for Testing and Materials under ASTM standard E1557. The UNIFORMAT II standard utilizes elements that are traditionally defined as major construction system components, common to most buildings that perform a given function regardless of the design specification, construction method or materials used. The UNIFORMAT standard provides a common organizing framework linking the building program, specifications, and estimates for a commercial construction project. While the UNIFORMAT standard provides a structure for organizing building elements and construction costs in commercial construction projects, there exists no such standard for the organization of building component elemental classifications and construction costs in residential projects.
Typical construction estimating practices are organized into 3 methodologies. Their use is typically determined by where in the design development process the estimate is occurring; Early, Mid or Final stage. Early stage estimates are most commonly based on a “rule of thumb” average cost per square foot of finished construction area (Cost/SF). This process is highly inaccurate and is the most frequently and easily misapplied method of estimating. It does not model the cost for any specific project and it does not adequately factor the variables for costs of unfinished construction (areas without finish, such as garage and unfinished basement) or adequately factor the variables of different quality levels of construction. Furthermore, it is inherently unable to model costs uniquely relevant to any given project. Early stage estimates may also be based on a historical cost per square foot of finished construction area (Historical Cost/SF) for similar projects. Here costs are derived based on a database or factors of similar type projects but again result in poor accuracy as this methodology is also inherently unable to model costs uniquely relevant to a subject project. This process is also limited by the extent of a given historical database having a very close “historical project” to the subject project being estimated. If the subject project is different than the historical projects, this process is no better than the Cost/SF method.
Mid to Final design stage estimates are based on the traditional detailed Quantity Take-Off (QTO) and unit price estimate method. This process is extremely time consuming and tedious, yields a more accurate cost of a subject project than the previous two methods, but is only able to be performed with significantly complete blueprints and specifications. It requires completed detailed and scaled drawings, notes and specifications to allow the estimator to calculate areas, quantities and to determine quality levels. This method cannot be used for early stage estimates/budgets since the design must be significantly complete and drawn before the estimate can be performed. Any change to the design results in drawings having to be redone and the QTO estimate recalculated.
None of these common estimating practices are able to accurately estimate the costs of construction for a residential project at any point in the design development process (Early, Mid or Final stage), nor are they able to dynamically model the cost impacts of variations to size and quality levels of construction components such that a specific estimate for a unique residence may be derived.
The computer-based residential cost estimation process of the present invention allows the ability to vary the selections related to design decisions, components of construction, quality of construction components, size of the home, quantities of materials and other variables within dynamically linked logical arguments in the computer program, resulting in instant recalculation of quantities and cost. This feature provides the ability to model numerous design and construction quality options, and to determine the cost impact of those options, so that a consumer may determine the cost of a residence or define the design parameters of a residence to meet a predetermined budget.
This invention is unlike other current estimating technologies which are based on manual or Computer Aided Design (CAD) quantity take off methods (QTO) involving computer calculations of areas and quantities of materials derived from fully developed design documentations; or based on a database of “similar” type projects of limited similar attributes to a subject property. This invention provides the technology unlike any other to instantly model the cost of a specific residence to specific design criteria at any stage of design.
The cost estimating structure of this invention is based on a unique building component elemental classification structure emulating the UNIFORMAT elemental classifications standard for only the construction system and select subsystem titles, but include further functionally descriptive materials such as assemblies and subassemblies of construction that are unique to residential buildings. UNIFORMAT is a system for classifying building products and materials by functional system, (e.g., substructure, superstructure, exterior closure). Other estimating structures based on quantity take off methods (QTO) use the Construction Specifications Institute (CSI) 16 Division MasterFormat structure that is organized according to construction trade divisions based on construction products and materials. UNIFORMAT structure differs from trade bid structures because it is based on a building systems/subsystems classification structure instead of a product classification system (CSI MASTERFORMAT Divisions 1-16). Trades for multiple CSI Divisions may show up in a given UNIFORMAT system, (e.g., UNIFORMAT System 043-Exterior Doors includes labor, products and materials from multiple trade divisions such as door, hardware, door carpentry framing, exterior and interior trim casings, caulk, weather stripping and painting). The CSI MASTERFORMAT structure is reasonable for final stage QTO estimates based on fully developed and detailed architectural and engineering blueprints and specifications. However, it is inadequate and inappropriate for early or mid stage estimating when drawings are incomplete and when economic comparisons of design alternatives are still being made. Significantly, it is in the early stages of design when reliable cost information on alternatives is most important yet is most difficult to achieve. The satisfaction of that need is one of the advantages of this invention. With the unique elemental classification structure of construction assemblies embodied in this invention, a user is provided the cost data usefully structured, and in real-time, so that economic analysis of design options may be understood.
This invention is a computer based construction estimating process and software, similar in function to a “rules based expert system”, allowing analog and digital modes of data collection (e.g., paper or web based interface) and digital and physical user interface of data input (e.g., web based interface or physical input into computer). The present invention fills a significant real world need of providing a means for reliable residential cost estimates for a unique residence at any stage of the design or development process.
Advantages of the present invention include: 1) the ability to estimate costs at any stage of the design development process 2) not based on inaccurate “rules of thumb” estimating practices embodied in cost per square foot ($/SF) of finished construction but rather is based on total finished living area of the residence and the total constructed area of the residence which includes unfinished/non-living areas such as garage, unfinished basement 3) Not based on limiting “similar project databases” but rather on criteria specific to a particular house 4) Intelligent and dynamic allowing effects in cost from changes to any part of the design to be immediately understood and calculated 5) Reliable enough to be used as a cost breakdown for bank financing 6) Computer based construction estimating process is designed to work with an organized and similarly structured data collection tool (e.g., paper or web based interface) allowing consistent data collection to occur in a number of modes including: a) person to person b) remote completion of paper based data collection tool c) internet based completion of electronic data collection tool which directly inputs selections into model.
The Computer based construction estimating process provides functional descriptive output material of sufficient detail that it is used to define building specifications which are directly derived from project criteria and component options selected in development of the cost estimate, as well as the following advantages: 1) Robust ability to model “virtual geometry” of the residence driven by numerous combinations and options of residential home design elements comprising: House style (1 story; 1½ story, 2 story); Roof style (hip/gable) and use of secondary major gable ends; Varying roof pitch; Varying roof overhang; Use of dormers on house and garage; Use of chimney structure(s); Aspect ratio (length to width) of home; Use of covered porch; Use of screened porch; Structural system of home (dimensional framing versus post and beam) and ability to change structural system between major residential elements such as the main house, breezeway, garage; Establishment of individual ceiling heights for all floors of structure; Square foot areas of ground floor elements with areas of upper floor areas driven by the logical arguments of the formulas and prior selections or as modified input from the operator; Window areas; Use of 2 story open space when required; Inclusion or not of vaulted ceiling space for major residential elements of the main house, breezeway, garage; Basement usage including no basement, partial basement, full basement, crawl space and ability to model various basement conditions under major residential elements of the main house, breezeway, garage; Attached or detached garage options, connected or not connected by a breezeway; and Use of “shelled” spaces, i.e., constructed but unfinished areas (which will affect quantity and cost output later in the model).
The process also has the robust ability to model various materials of construction and construction assemblies for the residence and related site-work, through the use of expert system formulas and the ability to permanently include within the component options and cost database, new selections that may be required on a specific residence.
The process of the present invention uses “If-Then-Else” rules of the expert system formulas and are “self-correcting” in that they contain the logical arguments necessary to prevent faulty inputs and selections from being made, alerting the user to unacceptable or non-normal selections. The process also includes “If-Then-Else” rules of the expert system formulas that are “self-directing” in that they contain the logical arguments necessary to enable or preclude other pre-written options from being selected.
Building component elemental classifications are unique and improved over prior technology in that they are based on UNIFORMAT for only the construction system and select subsystem titles but create functionally descriptive material including: New assemblies and subassemblies of construction unique to residential buildings; Cost summary that relates to a standard breakout of costs for the immediate residence and for ancillary residential project costs including site-work and equipment costs. The process has the ability to dynamically model building costs of specially finished spaces at a detailed room by room level providing significant functionality to the model to vary finish materials and sizes of specially finished spaces, thereby providing a more accurate determination of construction costs. The process also has the ability to model geometry, structural systems, various materials of construction and construction assemblies for the residence and related site-work through the use of dynamic expert system formulas that make unnecessary the requirement for generic “Special Construction” categories which require manual input of values as in other estimating systems.
Other advantages of the present invention include: 1) Provisions for user overrides of computer generated quantity default values; 2) The ability to model alternative building selections and resulting costs from a baseline set of selections and resulting costs (required to allow “what-if” option evaluations) and have the computer instantly self document the line item cost impacts of specific changes as they are being made in the alternate mode; 3) Extensive functionally descriptive material database of unit prices used in the calculation of costs include consideration of, and ability to change important factors within the unit price calculations, such as sales tax and subcontractor general conditions; 4) Extensive functionally descriptive material database of unit prices used in the calculation of costs allow the ability to modify sales tax, subcontractor general conditions and geographic location factors (reflecting local market conditions) at a line item level within the unit price database; 5) Extensive functionally descriptive material database of unit prices for components are not comprised of static numbers but are dynamically linked to further supporting functionally descriptive databases of components including subassemblies of the component and costs of the subassembly including labor and material, resulting in the ability to adjust or document the component's unit price; and General Contractor's “General Conditions, Overhead and Profit” are dynamic options and provide ability to model variations to the General Conditions, Overhead and Profit components of the Contractor's cost.
There is therefore a need for a residential cost estimate process that can accurately and dynamically model a plurality of design and construction quality options at any stage during the design development process to determine the cost impact of those options, such that a consumer may determine the cost of the residential structure unique to their specific requirements and be able to define, model and change the home's various design characteristics, components and quality levels of those components to meet a predetermined target budget.